1298329 Master & slave clock systems TRI-TECH Inc 7 Oct 1970 [14 Oct 1969 12 June 1970] 47784/70 Heading G3T In a master and slave clock system, a master unit responsive to the frequency of a timing signal source (e.g. A.C. mains frequency or alternatively a crystal or tuning fork controlled oscillator) supplies pulses at a lower frequency to a plurality of slave clocks comprising stepping motors. The slave clocks may be powered from respective local D.C. sources triggered by the pulses or the pulses may have sufficient energy to drive the motors in discrete steps. All the motors of the slave clocks may receive a drive pulse either simultaneously, or successively so that only one slave clock is moved at a time. The pulses from the master unit may be transmitted by line or by radio link. Stand-by power supply may be provided in the event of mains failure. In one embodiment, Fig. 9, the master unit includes a permanent magnet balance wheel 402 with hair spring 408 and loosely coupled magnetically to a permanent magnet rotor 404 of a stepper motor 406 so as to oscillate at a predetermined natural frequency which is a submultiple of the mains frequency. A pick-up coil 414 adjacent the balance wheel applies signals at the oscillation frequency to an electronic circuit 416 which amplifies the signals and uses them to pulse the stepper motor and sustain the oscillations of the balance wheel. The coil 414 is coupled via a relatively high resistance 422 to the A. C. mains so as to impress upon the signal induced in the coil a small A.C. voltage synchronized with the mains frequency. The stepper motor 406 also drives a shaft 430 coupled to a clock movement 432 whereby to rotate time indicating hands 436. In addition the shaft 430 has a right angled end 438 which engages a crank 440 to rotate a permanent magnet rotor 444 of a pulsing generator 442. Thereby pulses are induced in field coil 454 which are amplified and applied to operate slave clocks 460 simultaneously. The balance wheel 402 may be held stationary by a solenoid during normal operation, the voltage from the mains via R422 ensuring that the stepper motor 406 rotates synchronously or at a submultiple of the supply frequency. In the event of a mains failure the solenoid releases the balance wheel and the timing circuit 416 will operate independently of the mains being powered by a battery 418. Alternatively the master unit may comprise a synchronous motor driven by the mains and rotating a permanent magnet which co-operates successively with a plurality of reed switches as illustrated, Fig.3 (not shown) whereby to send pulses successively to the slave clocks, or the motor may rotate a light source and mirror to successively actuate photo-cells (not illustrated) and supply pulses to the slave clocks. In further alternatives the master unit may produce the timing pulses electronically, e.g. as Fig. 4 (not shown) wherein each slave clock is connected to a respective output of a ring counter driven by squarewave pulses from a storage counter which steps down the frequency of and converts the sinusoidal mains supply to squarewave. Or as illustrated in Figs.5 and 6 in which a pulsing circuit counts the cycles from the A. C. supply and produces squarewave output pulse each time a predetermined number has been counted. The pulsing circuit comprises a frequency divider arrangement including a series of six bi-stable flip-flops the output of each of which is applied to a NAND gate. The output signal from the gate turns ON a respective transistor T2 in a trigger circuit, Fig.6, to momentarily connect a battery 118 to the respective slave clock motor 120 and advance it one step. In the intervals between the timing pulses the NAND gate supplies low level D.C. charging current to the battery. Alternatively there may be one large battery in the master unit whereby the master unit can supply pulses of sufficient energy to drive the slave clocks. The master unit of Fig.5 may include a radio transmitter to transmit the pulses and each slave clock have a respective radio receiver, as illustrated, Fig. 7 (not shown). In embodiments, Figs.8 and 8A (not shown) the master unit includes a permanent magnet balance wheel coupled to a drive coil and a pickup coil in a feedback circuit to sustain oscillations. Also the balance wheel shaft drives through gears a permanent magnet rotor which induces pulses in a further coil, which pulses are amplified to actuate slave clock motors. The slave clocks may be elapsed time indicators, a clock with hands, or digital indicator, a time switch, a repeat cycle timer, or a time delay relay or a chart drive.